89Zr-Trastuzumab PET/CT for Detection of Human Epidermal Growth Factor Receptor 2–Positive Metastases in Patients With Human Epidermal Growth Factor Receptor 2–Negative Primary Breast Cancer

This second group of patients confirms the proof of concept that Zr-trastuzumab PET/CT detects unsuspected HER2-positive metastases in a subset of patients with HER2-negtive primary breast cancer. False-positive Zr-trastuzumab-avid foci present a challenge to using this tracer.